As shown in FIG. 1, a nuclear power station conventionally includes a reactor pressure vessel 10 sealed within a containment structure 50 that houses several power-producing systems and equipment. Reactor 10 may include various configurations of fuel and reactor internals for producing nuclear power. For example, vessel 10 may include several fuel assemblies positioned within a general cylindrical core. Fluid coolant and/or moderator may flow through reactor 10; for example, in US light water reactors, the fluid may be purified water, in natural uranium reactors, the fluid may be purified heavy water, and in gas-cooled reactors, the fluid coolant may be a gas such as helium, with moderation provided by other structures.
Vessel 10 may be sealed and opened through upper head 95 at flange 90. As shown in FIG. 1, during plant fabrication and at regular service and/or refueling outages, upper head 95 may be removed and operators and/or equipment can access internals of vessel 10 inside of containment structure 50 for various purposes. For example, with access to the reactor internals, some of fuel bundle assemblies may be replaced and/or moved between within the core and a fuel staging or spent fuel pool area(s), and maintenance/installation on other reactor structures in containment 50 may be performed.
During such maintenance, a refueling cavity 20 above flange 90 and surrounding reactor 10 may be filled, or flooded, with fluid coolant. The fluid coolant may both remove heat and block radiation from escaping to operators around cavity 20, such as workers performing maintenance on operations floor 25 above cavity 20. With such shielding, refueling cavity 20 may be used for storage of radioactive structures and a staging area for fuel handling, as well as a general interface for access into reactor 10.
Refueling bridge 1 with mast 3 and grapple 4 are useable during outages with access to reactor vessel 10 to perform fuel offloading, reloading, shuffling, and/or maintenance. Refueling bridge 1 may be positioned on operations floor 25 above or about flange 90 when reactor vessel 10 is opened. Bridge 1 may include a trolley 2 capable of rotating and/or laterally moving to any horizontal or vertical position. Trolley 2 may include a refueling mast 3 with hoist box and grapple 4 that descend into reactor 10 and perform fuel and other structure movements throughout cavity 20 during outages.
At other outage periods and during operations, cavity 20 may be drained completely or partially (such as down to flange 90). Because cavity 20 may have previously been flooded with fluid coolant before such draining, residues from and particulates in the fluid coolant may adhere to cavity surfaces, including cavity walls 21. These remnants from the fluid may be undesirable—such as radioactive or chemically corrosive—for operating conditions within cavity 20, on operations floor 25, and/or anywhere throughout containment building 50. As such, operators sometimes take measures to reduce particulates and impurities in any fluid that fills cavity 20. For example, plant operators may add solvents or otherwise change coolant chemistry to reduce deposition on surfaces drained of coolant and/or may use submersible, stationary filters on a floor of cavity 20. For example, underwater filters from Tri Nuclear Corporation may sit on a bottom of cavity 20 and filter or demineralize fluid in cavity 20.